ABSTRACT: Bone is a favored organ for the secondary growth from prostate cancer (PCa). Metastatic PCa is lethal and the mechanisms that drive its progression in the skeleton and contribute to the evasion of therapy are not understood. It has been recognized that interplay of PCa cells with the bone microenvironment is one of the key factors responsible for the adaptive pro-survival signaling in the metastatic tumor. Our own preliminary data show that in the fat cell-rich environments such as bone marrow, bi-directional cross-talk between metastatic tumor cells and fat cells results in key metabolic changes in both cell types, ultimately affecting tumor growth, survival and response to therapy. The key consequences of this cancer cell-initiated paracrine crosstalk are 1) altered oligomerization and activity of pyruvate kinase M2 (PKM2); 2) enhanced transcription of interleukin 1b (IL-1b) ; and 3) tumor survival-promoting changes in the mitochondrial iron metabolism. Our central hypothesis is that: tumor cell-adipocyte interactions enhance metastatic progression, while simultaneously reducing response to current treatments, by co-opting enzymatic and transcriptional activities of PKM2 and IL1b-mediated regulation of iron metabolism. We propose a multi-faceted approach that includes mouse models of lipolysis, 3D culture techniques, patient samples and PDX models, as well as state-of-the-art proteomics and RNAseq approaches to examine previously unexplored mechanisms linking lipolysis with PKM2/IL1?-mediated survival. We will perform these studies in three Aims. In Aim 1 we will conditionally delete adipocyte triglyceride lipase (ATGL) in adipocytes and study the molecular mechanisms of lipolysis on tumor progression in bone and response to docetaxel. In Aim 2 we will focus on lipid-mediated effects on PKM2 oligomerization. We will use proteomics approaches to map S-acylation sites on PKM2 and determine how this lipid modification regulates protein kinase activity and the phosphoproteome of the tumor to support growth and progression. In Aim 3 we will examine transcriptional targets of PKM2/IL-1b axis and its role in regulation of mitochondrial iron metabolism in PCa cells upon adipocyte exposure. Together, these aims provide independently valuable and novel information into the biology of bone marrow adipose tissue and its functional role in regulating the bone tumor microenvironment and metastatic progression. Our work will reveal new mechanisms of tumor adaptation and survival in bone and identify novel, mechanistic targets for therapy.